1. Field of the Invention
The invention relates to nanoelectromechanical devices and methods as applied to biological or medical
2. Description of the Prior Art
There have been a number of recent advances in NEMS and in Chemical Force Microscopy (CFM). NEMS approaches have resulted in a family of cantilevers of small length and thickness that can resonate at high frequency with high Q. When operated in ideal conditions (low T, vacuum) these NEMS devices show unprecedented sensitivity. “NEMS” in this specification is used to mean devices with at least one dimension which is equal to or smaller than one micron. It does not exclude the possibility that the “NEMS” device may have one or more other dimensions larger than one micron. Furthermore, as can be understood there is often no sharp line of distinction between the characterization of a device at or below one micron in size and one which is above one micron. The more meaningful significance to the term, “NEMS” is that the device in question shares some characteristic with similar devices scaled to submicron sizes or which is unique to submicron devices or operation.
On a much larger size scale (Atomic Force Microscopy (AFM), CFM) work in several groups has been directed at analyzing the forces exerted by interactions between single molecules, ranging from hydrogen bonds and antibody-antigen interactions to covalent bonds. AFM cantilevers, decorated with biomolecules and interacting with derivatized surfaces or with derivatized magnetic beads, demonstrate forces of order 100 pN for an antigen-antibody interaction and ˜1-10 nN for a covalent bond. These watershed experiments show the feasibility of measuring chemical events at the stochastic limit, but also offered evidence of the difficulty of harvesting this potential in a small, portable and robust device.
According to the invention what is needed is some way of reducing the size of the cantilever to NEMS dimensions to offer the needed temporal response, small volume and sensitivity to single molecules needed to build a device with single cell capability. Of course, placing a NEMS cantilever in solution and at room temperature will call for a revision of detection strategy from those usually employed for either CFM or NEMS. The fluid will damp the NEMS cantilever making resonance detection impossible, and the thermal energy of the solution will buffet the cantilever.
What is needed is some way to exploit these to potential difficulties as an integral part of the assay.
In contrast to conventional CFM what is needed according to the invention is an approach which will not attempt to measure the force of a single (or small number of) chemical bond by recording cantilever deflection.
What is needed is some type of design for a NEMS cantilever will allow detection of the presence of a chemical bond by the restriction it produces in the otherwise large thermally driven motion of the cantilever using an integral sensor.
What is further needed according to the invention is a means of using an array of BioNEMS cantilevers with systematically different chemical decorations offers both high reliability and sensitivity to concentration.
Further, according to the invention what is needed is some way of interpreting the “noise” of fluctuations as signal, and biology the opportunity of assembling and employing a useful and robust assay.
Microarray technologies have provided significant recent advances in analyzing protein receptors and their ligands, as well as in analyzing gene expression profiles. For example, microarrays of a few thousand targets have become a major technique used by the drug discovery industry. These microarrays are created by photolithography, by microstamping, or by microdotting, resulting in an array of spots (20-100 □m) on a substrate. The array is typically read by superfusing a fluorescently labeled analyte, over the array and determining the amount of binding by scanning the array with a micro-fluorimeter. Although these approaches are becoming increasingly widespread, the large size of the reader instrumentation and the intrinsic limitations of the fluorescence analysis employed make them completely inappropriate for applications in which both portability and robust performance are required. Furthermore, they are single-use devices, hence they cannot easily accommodate applications that require continuous monitoring. Finally, the devices rely on significant volumes of analyte, making them ill-suited to the most powerful recent advances in drug discovery provided by combinatorial chemistry or to the most sensitive assays of gene expression.
Another goal of the proposed studies is to develop a new technology of biochips at the nanoscale (BioNEMS) that is capable of sensing the binding of single biological molecules to their receptors. A growing literature of chemical force microscopy (CFM) has shown that a modified AFM can be tailored to measure the binding force of interactions ranging from single hydrogen bonds and single receptor-ligand interactions to single covalent bonds. The range of these forces are well within the capability of AFM instrumentation to detect; however, an AFM cantilever in solution does not have the temporal response characteristics needed to permit the binding and unbinding of biological ligands and their receptors to be followed reliably. Perhaps even more significant is the substantial size of the equipment required for performing AFM/CFM, and the well-known sensitivity of AFM to air-borne and surface vibrations.
What is needed is some type of technology that has the same success as CFM in detecting the forces of single molecular interactions, but is scaled down to NEMS scale to permit it to respond rapidly enough to follow the binding and unbinding events. Given the size of the chemical forces, the most robust mode for the BioNEMS to operate will be to forsake direct measurements of the force of binding. What is needed according to the invention is some type of means for using the ongoing fluctuations in the position of the NEMS cantilever followed using integral sensors to obviate the need for the support equipment used in AFM.